[InstCombine] Simplify gep (gep p, a), (b-a)

Patch by Andrea Canciani.

Differential Revision:  https://reviews.llvm.org/D27413

llvm-svn: 292506

1 files changed, 13 insertions, 19 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index f6d1a1e9664..24517a848ba 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1559,27 +1559,21 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
       // Replace: gep (gep %P, long B), long A, ...
       // With:    T = long A+B; gep %P, T, ...
       //
-      Value *Sum;
       Value *SO1 = Src->getOperand(Src->getNumOperands()-1);
       Value *GO1 = GEP.getOperand(1);
-      if (SO1 == Constant::getNullValue(SO1->getType())) {
-        Sum = GO1;
-      } else if (GO1 == Constant::getNullValue(GO1->getType())) {
-        Sum = SO1;
-      } else {
-        // If they aren't the same type, then the input hasn't been processed
-        // by the loop above yet (which canonicalizes sequential index types to
-        // intptr_t).  Just avoid transforming this until the input has been
-        // normalized.
-        if (SO1->getType() != GO1->getType())
-          return nullptr;
-        // Only do the combine when GO1 and SO1 are both constants. Only in
-        // this case, we are sure the cost after the merge is never more than
-        // that before the merge.
-        if (!isa<Constant>(GO1) || !isa<Constant>(SO1))
-          return nullptr;
-        Sum = Builder->CreateAdd(SO1, GO1, PtrOp->getName()+".sum");
-      }
+
+      // If they aren't the same type, then the input hasn't been processed
+      // by the loop above yet (which canonicalizes sequential index types to
+      // intptr_t).  Just avoid transforming this until the input has been
+      // normalized.
+      if (SO1->getType() != GO1->getType())
+        return nullptr;
+
+      Value* Sum = SimplifyAddInst(GO1, SO1, false, false, DL, &TLI, &DT, &AC);
+      // Only do the combine when we are sure the cost after the
+      // merge is never more than that before the merge.
+      if (Sum == nullptr)
+        return nullptr;
 
       // Update the GEP in place if possible.
       if (Src->getNumOperands() == 2) {